Color reproduction



Nov. 29, 1966 E. R. ATKNSON' COLOR REPRODUCTION Filed Oct. 20, 1965INVENTOR. EDWARD R ATKINSON FIG. 2

A TTORNE Y United States Patent 3,288,059 COLOR REFRODUCTION Edward R.Atkinson, 366 S. Troy St., Aurora, Colo. Filed Oct. 20, 1965, Ser. No.506,419 3 Claims. (Cl. 101211) This application is acontinuation-in-part of my application entitled Photographic ColorReproduction, Serial No. 329,897, filed August 28, 1964, and nowabandoned.

This invention relates, in general, to color reproduction printing andmore particularly, to a method of gravure or intaglio printing involvingthe use of a specially formed and correlated set of screen-pattern,separation printing plates, which may be readily engraved byconventional engraving apparatus.

In color reproduction printing, it is conventional to etch the printingsurface of each of the correlated printing plates to provide circular orrectilinear patterns in the order of 120 wells or cells per inch or 1440wells per square inch. Either all wells are provided with the sameoutline having the same surface area in which the light tones areproduced by varying the depth of the wells, or alternatively, the depthof the wells remains constant and the surface area of the wells isvaried. .Both of these methods of achieving differences in shade or tonein color reproduction printing are quite conventional and are set forthin United States Patent 923,799 to C. W. Saalburg, issuing on June 1,1909. conventionally, well depth varies from 35 microns for solid colorsto 2 microns for the light color tones or tints. The principaldisadvantage to varying the depth of the well is that the extremelyshallow wells change rapidly in volume as the printing surface wears,thus resulting in frequent and costly make overs. Further, since each ofthe wells is separated by a solid printing surface section known as abridge, no ink transfer is provided from the printing plate to the paperat the areas of contact between the paper and the bridge surface. Due tothe small size of the individual wells, the presence of the bridges, thewear on the plate and the shallow depth of some of the wells, and theinability of the capillary attraction to adequately remove all of theink from the well during the process of transmitting ink from the wellto the paper, pickiness or mealiness results. In this case, the inkitself acts in the nature of adhesive tending to tear during contactbetween the paper and the printing surface whereby only part of the inkcarried by the well is transferred to the paper, while the remainder ofthe ink remains within the shallow, small area well, thus greatlyincreasing the possibility of a poor quality color reproduction clue tothe presence of the unwanted pickiness. Pickiness is particularlyobjectionable for those areas of the color image involving the yellowprimary color ink.

In addition, in conventional multicolor photoengraving practice, it hasbeen found that a color image reproduced by the superpositioning ofimprints from a plurality of screen-pattern, color-separation platesoften is impaired by objectionable interference or moire patterns. Thesepatterns result from the impracticability of similarly, preciselyregistering the corresponding ink patterns of the several screen-patternplates and manifest themselves by the appearance of an objectionable:grid pattern with a distinct geometric design, and also by actual colordistortion. In multicolor photoengraving, one solution of the problemdescribed involves the exposure of each of the color-separation platesto light reflected from a specially prepared blaok-and-white separationplate with a conventional ph-otoen-gravers screen interposed to producethe desired screen effect in the image. The screens are rotated throughdifferent angles relative to a horizontal base line for the severalexposures so that the lines of the screen-patterns fall at diflferentangles relative to such a base line. A group of color-separation platesso formed is capable of printing a color reproduction with a minimum ofobjectionable moire patterns.

In order to increase the reliability of the color reproduction, theyell-ow primary color image must be emphasized since it is highlysusceptible to dilution by the presence of the other primary color imageportions; that is, the :blue and the red. In the past, this has beenachieved principally by increasing the depth of the wells carrying theyellow ink to ensure a heavy tone yellow ink pattern.

It is, therefore, a primary object of this invention to provide a newand improved color reproduction printing method which employs acorrelated set of screen-pattern, color-separation printing plates whichcompletely eliminates objectionable mealiness or pickiness normallyassociated with multicolor image reproduction.

It is a further object of this invention to provide a new and improvedcolor reproduction printing method which completely eliminates the needof angling of the screens in the production of all primary color dotscreenpattern plates whereby the primary color ink dot patterns are allprinted in parallel line fashion but deposited in nonsuperimposedfashion upon the ink receiving web.

It is a further object of this invention to provide an improved methodof color reproduction printing employing a correlated set ofscreen-pattern, color-separation printing plates which greatly reducesthe number of bridge lines per unit of service area, while eliminatingthe objectionable in-line pattern normally produced thereby.

It is a further object of this invention to provide a new and improvedcolor reproduction printing process producing a color image consistingof nonsuperimposed dots of the different primary colors in which thesurface area of yellow ink dots is in the order of twice the surfacearea of either the red or the blue primary color ink dots.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

In the drawings:

FIGURE 1 is a top plan view, greatly magnified, of a portion of a paperstock web after receivinga multicolor image consisting of ink dots ofthe primary colors and black ink dots at some angle thereto. 7

FIGURE 2 is a side elevational view of a preferred embodiment of thepresent invention showing the correlated set of screen-pattern,color-separation printing plates produced by conventional engravingmeans 'operatively positioned to provide the multicolor reproductionshown in FIGURE 1.

FIGURES 3A, 3B, 3C and 3D are plan views of the paper web showing theapplication of the multicolor ink dots in rectangular pattern as thepaper moves sequentiaL ly with respect to the correlated set ofscreen-pattern, color-separation printing plates of the apparatus shownin FIGURE 2 In general, the method of the present invention involves theuse of improved, correlated screen-pattern, colorseparation printingplates with the ink receiving wells formed therein in accordance withthe area to be printed and of an ink capacity in accordance with thedesired tone depth to form a first series of rectilinear ink dots ofalternater red and blue primary color ink, in line and at the sameangle, with the dots having a ratio of width to height of at least 2 to1 and being separated by relatively thin bridge lines. A second seriesof rectilinear ink dots of yellow ink is formed with the series of dotsbeing oriented parallel to the series of the red and blue ink dots andof like configuration to the red and blue dots,

for positioning in series fashion, on either side of the series of redand blue ink dots. The primary color ink dots are then deposited innonsuperimposed fashion on an ink receptive media, preferably with thebridge lines between dots for any given line of dots being offset withrespect to thebridge lines of the next successive line of dots. Further,to modify the color tone of the color reproduction image, the volume ofink carried by each dot is preferably varied without changing the dotsurface area. For four color printing, a fourth printing surface isprovided in which the wells are arranged in a rectilinear pattern againhaving one surface dimension in the order of twice the other surfacedimension but with the longitudinal axis of the line of wells beinginclined with respect to the longitudinal axis of its printing plate,whereby the black ink dots formed thereby are superimposed over the inkdots formed by the primary colors during sequential contact of the webwith the printing plates. 7 Referring to FIGURE 1, there is shown a planview of a paper web or print stock W. The section-shown in FIGURE 1 isgreatly magnified with respect to that shown in FIGURES 3A, 3B, 3C and3D. It should be remembered that there are a great number of ink dotsformed within any square inch of image receiving surface and asindicated previously, in conventional practice, the ink dot pattern isnormally in the order of 120 dots per inch, or 14,400 dots per squareinch. In this case, the present correlated set of color-separationprinting plates produce ink dots in the order of'225 dots per squareinch. A series of blue ink dots 10, yellow i-nk dots 12, red ink dots14, and black ink dots 16 are produced. They are separated fromthem-selves by bridge lines 18 which are transverse to thelongitudinalaxis of the respective dots and bridge lines 20. Bridgelines 20 extend longitudinally between respective dot lines, such asblue dots and yellow dots '12. The bridge lines 20 lie longitudinally ofthe axis of the series of individual color dots, such as the yellow dotswhich are positioned all in a, row with the exception of the narrowtransverse bridge lines 18. The red and blue ink dots are alternatelydisposed along a common base line and are separated by the thintransverse bridge lines 18. In the case of the four color multicolorimage reproduction systems, there is provided, in addition to theprimary color ink dots, black ink dots 16 which, in the presentinvention, are superimposed over the spaced primary color ink dots atsome angle to the longitudinal axis of the primary color dots normally45 thereto.

It is noted that it is a principal object of this invention to provide atrue color reproduction having the desired color balance. Knowing in thepast that emphasis was placed on the yellow ink pattern byusing-excessive well depth to provide a higher than necessary yellowcolor tone image, the present invention advantageously uses a system ofink dot distribution which involves parallel rows of rectilinear yellowink dots which sandwich rows of :in line, alternate red and blue inkdots, thereby providing in nonsuperimposed fashion what would appear tobe a solid pattern of the primary color inkdots in whichthe dot squarearea of yellow ink would be twice that of either the red or blue inkdots.

There are several dissimilarities from conventional practice which arequite obvious when viewing FIGURE 1. In order to reduce the number ofareas of the image copy not receiving ink, the present system employsink dots which are irregular rectangles, that is, they have one surfacedimension which is at least twice that of the other surface dimension.For instance, in all of the dots shown in the embodiment used to producethe image of the type shown in FIGURE 1, the width of the ink dots shownis three times as large as its height. In prior practice, it isconventional to provide ink dots resulting from ink wells or cellshaving rectangular or round configuration, but of equal surfacedimensions; that is, the wells are formed square rather than as shown.

The effect of the present arrangement is to cut in thirds the number oftransverse bridge lines 18, thus reducing greatly the areas of the imagereceiving medium which does not receive ink while enlarging each dotarea to eliminate pickiness. Further, the present image is characterizedby having primary color ink dots which are not superimposed upon eachother; therefore, the .red ink does not dilute the blue ink or the blueink dilute the red, for instance, nor does the blue dilute the yellow,the yellow the blue, or the yellow and red in the same fashion. This isachieved by employing a correlated set of screen-pattern,color-separation printing plates in which there is operative alignmentbetween the respective plates so as to deposit yellow rectangular inkdots in parallel fashion between the spaced blue ink dots 10, the dotsbeing separated axially of the web receiving the image by thin bridgingareas or lines 20. In addition, in an attempt, to reduce the area of thepaper not receiving ink due to the bridging lines between therectangular ink wells or cells, it is noted that the horizontal bridginglines 18 between the red and blue dots and the yellow dots are notaligned, but are longitudinally displaced such that the bridging lines18 between any two dots actually terminate adjacent the center line ofthe ink dot of the next succeeding line.

The production of a multicolor image in this fashion may be bestappreciated by reference to FIGURES 2, 3A, 3B, 3C and 3D which show theapparatus for producing multicolor image reproduction and the sequence,of printing of the multicolor image upon the web passing over therespective aligned, operatively connected printing plates.

separation printing plates indicated at 30, 32, 34 and 36; 30 being theblue printing plate, 32 the red printing plate,

34 the yellow printing plate and 36 the back printing plate.

Each of the cylindrical printing plates includes a source of inkindicated by a shallow pan 38, with the plate rotatpan filling theindividual rectangular wells 42, 42, 42" and 42". The cylinder rotatesto a point where a doctor blade 44 wipes the excess ink off-of theprinting surface 40 with ink filling the individual wells 42 in volumedepending upon the depth of the respective wells to produce the varyingcolor tints desired.

The wells 42 of the red printing cylinder 32 are of equal size to thewells 42 of the blue print cylinder 30 and are spaced axially a distanceslightly greater than the longitudinal surface dimension of each of thewells. The wells 42' are also positioned on plate 32 in predeterminedalignment with respect to the wells 42 of the blue print plate 30 so asto produce red dots which lie on the same rangement, and in fact,bridges in the order of inch in thickness may be used satisfactorily,thus effectively producing a bridge line, on the web being printed, oflike surface dimension for both the transverse bridge lines and thehorizontal bridge lines. This aids in eliminating pickiness as well asproviding a color reproduction print without a distracting patterneffect. This may be more readily appreciated by reference to FIGURE 3A,3B, 3C and 3D.

Reference to FIGURES 3A, 3B, 3C and 3D of the drawings indicates theposition of the ink dots as formed on web W, sequentially, 'as a resultof movement of the The embodiment of FIGURE 2 makes use i of acorrelated set of cylindrical screen-pattern, colorweb in a directionindicated by the arrow. Thus, as web W passes in contact with the blueprint cylinder 30, a series of blue dots are formed generally in a line,as indicated in FIGURE 3A. For the purpose of simplifying theexplanation, only a single line of spaced blue dots are showntransferred from .printing cylinder 30 to the web W. Of course, therewould be transferred a great number of dots, actually hundreds persquare inch. As the web moves from the blue print cylinder 30 to the redprint cylinder 32, red ink dots are formed intermediate of the .bluedots and in line therewith in the manner indicated in FIGURE 3B. Theblue ink dots and the red dots are separated only by thin bridging lines18, as best indicated in FIGURE 1. As the web moves further, yellow inkdots are transferred, from the respective wells 42" of the yellow printylinder 34, the individual dots 12 being all in line, separated fromthemselves in a transverse direction by the thin bridging lines 18 andaxially of the blue and red dots by thin bridging line 20 as indicatedin FIG. 3C. It is to be noted that the transverse bridging lines 18between the respective red and black and blue dots are not aligned withthe bridging lines 18 between the adjacent yellow ink dots 12.

As the web W moves to its final ink transfer, the black ink filling theline of ink wells 42" which are angled with respect to the axis of theprint cylinder 36 causes a series of black ink dots to be transferred tothe web, but unlike the previous inkdots, are superimposed and actuallyoverlie the blue, red and yellow dots and may act to dilute the ink ofthe respective primary color dots as indicated in FIG. 3D.

It is important to note that in the photoelectric etching process thefinal product is a series of correlated screenpattern, color-separationprinting plates having all the dots of the same surface area but varyingin depth enabling them to be rectangular in shape, separated by a bridgewhich create a fine bridge line which in turn enables the dot to ride onthe surface wiping the top of the cylinder clean as it emerges from theink foundation. The individual color printing plates 30, 32, 34 and theblack dot printing plate 36 are mechanically aligned and rotate inunison to produce the desired pattern shown in FIG. 3D. Mechanicalalignment is indicated schematically by the dotted line 50 in FIGURE 2.While the dots are shown having a horizontal surface dimension equal tothree times the vertical dimension, other ratios above 2 to 1 may beused, always reducing the number of transverse bridges below the numberrequired by the square or round wells of conventional processtechniques. As a result of the present process, the elimination ofscreen angles other than for the black ink dots, provide all of theprimary color dots in in-line fashion with the least moire or pattern,while the positioning of the transverse bridge lines 1-8 of any line ofdots at the center line of the next line of dots greatly reduces thepossibility of pickiness or mealiness while also contributing toreduction in noticeable pattern. While the invention is shown as appliedto a system in which variation in tone i achieved by varying the depthof the individual wells 42, 42', 42", 42 in respect to cylinders 30, 32,34 and 36, the eifect may be achieved by maintaining constant depth ofthe wells, maintaining the two or three to one dimensional variations ofthe rectangular wells but varying the overall surface area of theindividual wells depending upon the color tone desired.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinventlon.

What is claimed is:

1. The method of producing a color reproduction image which ischaracterized by lack of pickiness, minimum pattern and color distortioncomprising the steps of: printing a first series of alternate red andblue rectilinear ink dots, in line, and at the same angle on an inkreceptive media, with said dots having a ratio of width to height of atleast two to one, being separated by relatively thin bridge lines andwith said red and blue dots having the same surface area, printing onsaid media other series of rectilinear, in line ink dots of yellow ink,parallel to and on either side of said series of red and blue dots withsaid yellow ink dots being of like configuration to said red and blueink dots, with relatively thin bridge lines therebetween, and with thetotal surface area of the yellow ink dots being in the order of twicethat of either the blue or red ink dots and controlling the tone of theink dots by varying the volume of ink for respective dots.

2. The method as claimed in claim 1 further including the step ofpositioning adjacent series of rectilinear ink dots such that the bridgelines between dots for any given line of dots is offset with respect tothe bridge lines for the next successive line of dots.

3. The method as claimed in claim 1 further including the step ofmodifying the color tone of the color reproduction image by varying thevolume of ink carried by each dot without changing the dot surface area.

No references cited.

ROBERT E. PULFREY, Primary Examiner. JAYNCE A. BELL, Assistant Examiner.

1. THE METHOD OF PRODUCING A COLOR REPRODUCTION IMAGE WHICH ISCHARACTERIZED BY LACK OF PICKINESS, MINIMUM PATTERN AND COLOR DISTORTIONCOMPRISING THE STEPS OF: PRINTING A FIRST SERIES OF ALTERNATE RED ANDBLUE RECTILINEAR INK DOTS, IN LINE, AND AT THE SAME ANGLE ON AN INKRECEPTIVE MEDIA, WITH SAID DOTS HAVING A RATIO OF WIDTH OF HEIGHT OF ATLEAST TWO TO ONE, BEING SEPARATED BY RELATIVELY THIN BRIDGE LINES ANDWITH SAID RED AND BLUE DOTS HAVING THE SAME SURFACE AREA, PRINTING ONSAID MEDIA OTHER SERIES OF RECTILINEAR, IN LINE INK DOTS OF YELLOW INK,PARALLEL TO AND ON EITHER SIDE OF SAID SERIES OF RED AND BLUE DOTS WITHSAID YELLOW INK DOTS BEING OF LIKE CONFIGURATION TO SAID RED AND BLUEINK DOTS, WITH RELATIVELY THIN BRIDGE LINES THEREBETWEEN, AND WITH THETOTAL SURFACE AREA OF THE YELLOW INK DOTS BEING IN THE ORDER OF TWICETHAT OF EITHER THE BLUE OR RED INK DOTS AND CONTROLLING THE TONE OF THEINK DOTS BY VARYING THE VOLUME OF INK FOR RESPONSIVE DOTS.